Minkowski metric and proper time interpretation

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Discussion Overview

The discussion revolves around the interpretation of the Minkowski metric and proper time in the context of gravitational effects on time dilation, particularly near a heavy mass. Participants explore the implications of different metrics and their validity in specific scenarios.

Discussion Character

  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant suggests that a clock ticks slower near a heavy mass, interpreting proper time as represented by ##d\tau## rather than ##dt##.
  • Another participant challenges the initial assumption about the value of ##a## in the metric, stating that ##a < 1## for the Schwarzschild metric.
  • A participant references a metric from a book, indicating confusion about its application and validity, and questions its relationship to other sources like Wikipedia.
  • One participant clarifies that the discussed metric is local and only valid in a small region, emphasizing that the reference clock is at ##y=0##, with clocks at higher ##y## ticking faster and those at lower ##y## ticking slower.
  • A later reply indicates a realization of understanding following the clarification about the local metric.

Areas of Agreement / Disagreement

Participants express differing views on the interpretation of the metric and its implications for time dilation, with no consensus reached on the correct understanding of the metric in question.

Contextual Notes

The discussion highlights limitations in understanding the assumptions behind the metrics, the dependence on specific conditions, and the potential for confusion arising from different references.

msumm21
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TL;DR
I'm trying to learn general relativity, but misunderstanding how the metric implies that time appears to pass slower for something near a heavy mass, as viewed from something far away
Using an example of 1 space dimension and 1 time dimension, consider the metric ##d\tau^2 = a dt^2 - dx^2## near a heavy mass (##a>1##).

From what I've read a clock ticks slower near a heavy mass, as viewed from an observer far away. A clock tick would be representative of ##d\tau## right (not ##dt##)? If so, then my confused understanding is below.

If ##a## is large, then small ##dt## results in large ##d\tau##. If the far away observer's ##d\tau## is approximately ##dt##, then his clock tick, say ##dt=1## corresponds to ##d\tau >> 1## near the mass. My interpretation of this is that the clock near the mass ticks ##d\tau >> dt## ticks (it ticks more than the clock far from the mass), and hence the clock near the mass moves faster. I realize this is wrong, but not clear what part is wrong.
 
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Your basic assumption is wrong: ##a < 1## for the Schwarzschild metric.
 
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The book I'm reading (General Relativity: The Theoretical Minimum by Susskind) says the metric is approximately ##d\tau^2 = (1+2gy)dt^2 - dy^2## where the grav potential is ##gy## but yes I see this doesn't jive with stuff I see on Wikipedia. I must have misunderstood what this metric was supposed to be in the first place. Does anyone know what this metric is?
 
msumm21 said:
I must have misunderstood what this metric was supposed to be in the first place. Does anyone know what this metric is?
This is a local metric, only valid in a small region. The reference is not a clock at infinity, but a clock at ##y=0##. Clocks at higher ##y## will be faster and clocks at lower ##y## will be slower compared to the reference clock.
 
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Dale said:
This is a local metric, only valid in a small region. The reference is not a clock at infinity, but a clock at y=0. Clocks at higher y will be faster and clocks at lower y will be slower compared to the reference clock.
Oh yes I think I'm getting it now, thanks!
 
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